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3 Iterations Of BMW i3 And MINI Cooper SE Fast Charging Analysed

Here is how the curve changed, despite the power cap at 50 kW.

2018 BMW i3

Mark Kane

By: Mark Kane

Apr 22, 2021 at 12:17pm ET

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Today we will take a look a little bit into history and compare fast charging of three iterations of the BMW i3 (21.6, 33.2 and 42.2 kWh battery versions) and the related MINI Cooper SE model (32.6 kWh).

Those small electric cars are not expected to fast charge very quickly, but we would like to check whether BMW upgraded them in any way and what they offer. There are a few interesting findings in this report - small bricks in the foundation for further reports on newer models.

Data for this analysis comes from Fastned's fast-charging network, which is also an invaluable source for info about charging.

Let's first see the latest BMW i3 model, and then compare all four cars together.

Charging power vs state-of-charge (SOC)

The 2019 BMW i3 (44.2 kWh battery version) has a very flat charging curve with a peak charging power of 50 kW.

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State-of-charge (SOC) vs time

Charging from 20% to 80% SOC takes about half an hour.

Average charging power vs state-of-charge (SOC)

The average power in the very important range from 20% to 80% SOC is 47 kW, which is 94% of the peak value.

The flat charging curve and high average to peak power ratio indicate that the battery probably could charge much faster if only the charging system/all the onboard cables would allow for it.

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C-rate vs state-of-charge (SOC)

The peak C-rate* - charging power in relation to the total battery capacity of 42.2 kWh - is about 1.2C.

The average C-rate when charging from 20% to 80% SOC is 1.1C.

*C-rate tells us how the charging power relates to the battery pack capacity. For example: 1C is 1-hour charging power (current), when the power value in kW is equal to the battery pack capacity in kWh. 2C would be enough to recharge in half an hour.

The net battery capacity of 37.9 kWh stands for about 90% of the total battery capacity.

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Range replenishing speed vs state-of-charge (SOC)

The rate of replenishing range depends on the energy consumption and the energy consumption depends on the use case.

In the case of i3, we can compare the values for WLTP and EPA ratings:

WLTP
Taking into consideration the WLTP range of 310 km (193 miles) and available battery capacity of 37.9 kWh, we can assume energy consumption of 122 Wh/km (197 Wh/mile).
The effective average speed of range replenishing when charging from 20% to 80% SOC would be 6.4 km/minute (4 miles/minute).
EPA Combined
Taking into consideration the EPA Combined range of 153 miles (246 km) and available battery capacity of 37.9 kWh, we can assume energy consumption of 248 Wh/mile (154 Wh/km).
The effective average speed of range replenishing when charging from 20% to 80% SOC would be 3.1 miles/minute (5 km/minute).
EPA Highway
Taking into consideration the EPA Highway range of 136.4 miles (219 km) and available battery capacity of 37.9 kWh, we can assume energy consumption of 278 Wh/mile (173 Wh/km).
The effective average speed of range replenishing when charging from 20% to 80% SOC would be 2.8 miles/minute (4.5 km/minute).

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Comparisons with other EVs

2018 BMW i3

BMW i3

MINI Cooper SE Electric Collection

Comparison of charging power

The first comparison - of charging power curve - of three iterations of the BMW i3 and the MINI Cooper SE, reveals that BMW has increased the battery capacity (through using more energy dense cells), but probably did not touch the charging systems.

As a result, the power looks like it would be capped at 50 kW. We guess that the reason for that is to minimize costs on one hand and a conclusion that 50 kW for this type of cars is enough.

However, the charging curve has improved solely through the switch to a bigger battery capacity, because, as we can see, the bigger the capacity, the longer (to a higher SOC) the car was able to accept the peak value. The 22 kWh was falling at over 60% SOC, 33 kWh at around 80% SOC, while the 42 kWh was able to go up to almost 90% SOC.

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Comparison of C-rate

If the charging power is similar, then clearly the packs with higher capacity will be operating in "easy" mode, at under 1.5C, compared to the original 22 kWh battery (over 2C).

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A quick summary proves that the average charging power from 20% to 80% SOC improved with the increase of battery pack capacity. In the case of 2019 i3, it's 20% higher than in 2013 i3.

DC Fast Charging Comparison by InsideEVs Model
[data source] Drive /
Battery
(kWh) Max
Power Avg
Power
(20-80%) Max
C-Rate Avg
C-Rate
(20-80%) 2013 BMW i3 (22 kWh)
[Fastned] RWD
21.6 kWh 47 kW 39 kW 2.2 1.8 2017 BMW i3 (33 kWh)
[Fastned] RWD
33.2 kWh 50 kW 46 kW 1.5 1.4 2019 BMW i3 (42 kWh)
[Fastned] RWD
42.2 kWh 50 kW 47 kW 1.2 1.1 2020 MINI Cooper SE
[Fastned] FWD
32.6 kWh 49 kW 45 kW 1.5 1.4

Comparison of range replenishing speed

The speed of replenishing range is not particularly high, but high enough for the purpose of city cars that probably fast charge rarely.

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A quick summary also for various test cycles:

DC Fast Charging Comparison by InsideEVs Model
[data source] Drive /
Battery
(kWh) Avg
Power
(20-80%) WLTP range
rep. rate
(20-80%) EPA range
rep. rate
(20-80%) EPA Hgw range
rep. rate
(20-80%) 2013 BMW i3 (22 kWh)
[Fastned] RWD
21.6 kWh 39 kW N/A 4.5 km/min
(2.8 mi/min) 4.0 km/min
(2.5 mi/min) 2017 BMW i3 (33 kWh)
[Fastned] RWD
33.2 kWh 46 kW 7.2 km/min
4.5 mi/min 5.2 km/min
(3.2 mi/min) 4.6 km/min
(2.9 mi/min) 2019 BMW i3 (42 kWh)
[Fastned] RWD
42.2 kWh 47 kW 6.4 km/min
4.0 mi/min 5.0 km/min
(3.1 mi/min) 4.5 km/min
(2.8 mi/min) 2020 MINI Cooper SE
[Fastned] FWD
32.6 kWh 45 kW 6.1 km/min
3.8 mi/min 4.6 km/min
(2.9 mi/min) 4.3 km/min
(2.7 mi/min)

Conclusions

The conclusion from today's analysis is that the new BMW i3/MINI charges faster thanks to higher battery capacity, despite the charging system being capped at 50 kW.

Here is all the data for the currently available BMW i3 and MINI Cooper SE:

2019 BMW i3 :: DC Fast Charging Summary by InsideEVs
Drive: RWD; Battery pack (net / total): 37.9 / 42.2 kWh
[Data source: Fastned] Peak Power
Peak C-rate

Average Power (20-80% SOC)
Average-to-Peak Power
Average C-rate (20-80% SOC) 50 kW
1.2

47 kW
94%
1.1 Range Replenishing Speed (Average 20-80% SOC): WLTP
EPA Combined
EPA Highway 6.4 km/min (4.0 mi/min)
5.0 km/min (3.1 mi/min)
4.5 km/min (2.8 mi/min)

2020 MINI Cooper SE :: DC Fast Charging Summary by InsideEVs
Drive: FWD; Battery pack (net / total): 28.9 / 32.6 kWh
[Data source: Fastned] Peak Power
Peak C-rate

Average Power (20-80% SOC)
Average-to-Peak Power
Average C-rate (20-80% SOC) 49 kW
1.5

45 kW
92%
1.4 Range Replenishing Speed (Average 20-80% SOC): WLTP
EPA Combined
EPA Highway
InsideEVs 70 mph 6.1 km/min (3.8 mi/min)
4.6 km/min (2.9 mi/min)
4.3 km/min (2.7 mi/min)
4.6 km/min (2.8 mi/min)